The present invention relates to a multichamber base compartment two-compartment electrodialytic water splitter and a method of using same to produce an aqueous soluble basified salt solution and aqueous soluble acid at increased current efficiency.
Electrodialytic water splitting in a two-compartment cell is well known. For example, U.S. Pat. No. 4,391,680 filed by the same inventors discloses generation of strongly acidified sodium chloride and aqueous sodium hydroxide by two-compartment water splitting of aqueous sodium chloride. However, when generating strong bases in a two-compartment electrodialytic water splitter, the efficiency for base generation falls rapidly as the concentration of base in the base compartment increases due to migration of hydroxyl ions across the anion membrane from the base compartment into the acid compartment.
Various methods have been employed in the prior art in an attempt to overcome the decrease in current efficiency with increased concentration of base in the base compartment. For example, a three-compartment electrodialytic water splitter comprised of alternating bipolar, anion and cation permselective membranes thereby forming alternating acid, salt and base compartments is disclosed in our copending patent application Ser. No. 474,771, filed Mar. 14, 1983. In addition, the staging of two conventional two-compartment electrodialytic water splitters whereby the base solution withdrawn from the base compartment of one two-compartment water splitter is fed to the base compartment of a second two-compartment water splitter is known. In an attempt to increase the efficiency of the bipolar membrane, U.S. Pat. No. 3,111,472 (Oda et al.) discloses disposing a microporous water permeable cation or neutral membrane in the acid and/or base compartments of a three-compartment electrodialytic water splitter. However, Oda's apparatus and method does not overcome the lower efficiency due to migration of the hydroxyl ions through the membranes into the salt and/or acid compartments.
All of these prior art disclosures require installation of auxilliary equipment and separate additional process steps, both of which increase costs. In view of the foregoing, the industry has endeavored to develop a process capable of producing highly basic aqueous brine at low cell voltage. To date, this had not been achieved.